diff --git a/web_app/static/index.html b/web_app/static/index.html
index 0d56371..96ab59c 100644
--- a/web_app/static/index.html
+++ b/web_app/static/index.html
@@ -116,7 +116,10 @@ <h2 id="contentHeading">Lyrics</h2>
                                 </div>
                             </div>
 
-                            <button id="generateBtn" class="primary-btn">Generate Poster</button>
+                            <button id="generateBtn" class="primary-btn">
+                                <span class="btn-text">Generate Poster</span>
+                                <span class="spinner" style="display: none;"></span>
+                            </button>
                         </div>
                     </div>
 
diff --git a/web_app/static/script.js b/web_app/static/script.js
index 441a4ed..6549ebd 100644
--- a/web_app/static/script.js
+++ b/web_app/static/script.js
@@ -613,7 +613,31 @@ function handleLyricLineClick(lineNumber) {
 async function generatePoster() {
     if (!currentMetadata) return;
 
-    loadingOverlay.style.display = 'flex';
+    const btnText = generateBtn.querySelector('.btn-text');
+    const spinner = generateBtn.querySelector('.spinner');
+
+    const resetGenerateButton = () => {
+        generateBtn.disabled = false;
+        generateBtn.removeAttribute('aria-label');
+        if (btnText) btnText.style.display = 'inline-block';
+        if (spinner) spinner.style.display = 'none';
+    };
+
+    // Validate before setting loading state
+    if (currentMetadata.type === 'track') {
+        const startVal = parseInt(startLineInput.value) || 1;
+        const endVal = parseInt(endLineInput.value) || 1;
+        if (isNaN(startVal) || isNaN(endVal) || startVal >= endVal) {
+            showToast("Please enter a valid range (Start must be less than End).", "error");
+            return;
+        }
+    }
+
+    // Set loading state
+    generateBtn.disabled = true;
+    generateBtn.setAttribute('aria-label', 'Generating poster, please wait.');
+    if (btnText) btnText.style.display = 'none';
+    if (spinner) spinner.style.display = 'inline-block';
 
     const indexingToggle = document.getElementById('indexingToggle');
     const accentToggle = document.getElementById('accentToggle');
@@ -628,23 +652,12 @@ async function generatePoster() {
     };
 
     if (payload.type === 'track') {
-        // Lyrics Logic (Same as before)
         const startVal = parseInt(startLineInput.value) || 1;
         const endVal = parseInt(endLineInput.value) || 1;
-        const start = startVal - 1;
-        const end = endVal;
-
-        if (isNaN(start) || isNaN(end) || start >= end) {
-            loadingOverlay.style.display = 'none';
-            showToast("Please enter a valid range (Start must be less than End).", "error");
-            return;
-        }
-
-        payload.lyrics_start = start;
-        payload.lyrics_end = end;
+        payload.lyrics_start = startVal - 1;
+        payload.lyrics_end = endVal;
 
     } else {
-        // Album Logic
         payload.indexing = indexingToggle ? indexingToggle.checked : false;
     }
 
@@ -669,13 +682,17 @@ async function generatePoster() {
             posterContainer.innerHTML = '';
             posterContainer.appendChild(img);
             showDownloadButton(imageUrl, data.filename);
-            loadingOverlay.style.display = 'none';
+            resetGenerateButton();
+        };
+        img.onerror = () => {
+            showToast('Failed to load the generated poster image.', 'error');
+            resetGenerateButton();
         };
 
     } catch (error) {
         console.error("Generation failed", error);
         showToast(`Error: ${error.message}`, "error");
-        loadingOverlay.style.display = 'none';
+        resetGenerateButton();
     }
 }